Method for conditioning halogenated polymeric materials and structures fabricated therewith

ABSTRACT

A method of treating a halogenated polymeric-containing substrate including exposing at least portions of the halogenated polymeric-containing substrate to a composition containing a reducing agent and an aprotic solvent selected from the group consisting of nitriles, nitro compounds, amides, esters, carbonates, oxides, sulfo compounds and mixtures thereof. The solvent is free of ethers, amines, ammonia. The composition is prepared by reacting a metal with an organic compound selected from the group consisting of polyaryl compounds, aromatic carbonyl containing compounds, aromatic nitriles, and aromatic heterocyclic nitrogen containing compounds in a reaction solvent that does not react with the metal but permits reaction between the metal and the organic compound to thereby provide the reducing agent. The reducing agent is isolated from the reaction solvent to obtain a reaction product as a solid. The reaction product is added to the aprotic solvent. The treated substrate is contacted with a material to promote adhesion of the material to the treated surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of application Ser. No. 08/340,379 now abandoned,entitled Method for Conditioning Halogenated Polymeric Materials andStructures Fabricated Therewith, filed Nov. 14, 1994, which in turn is adivisional application of Ser. No. 08/013,652, filed on Feb. 4, 1993,and now U.S. Pat. No. 5,374,454, which in turn is a continuation of Ser.No. 07/584,327, filed on Sep. 18, 1990 and now abandoned.

DESCRIPTION

1. Technical Field

The present invention is concerned with conditioning halogenatedpolymeric materials to render them susceptible to being etched and/orcapable of having a conductive metal plated thereon including aconductive metal from an electroless plating bath. The present inventionis also concerned with a method for conditioning halogenated polymericmaterials to render such capable of being made conductive by doping.

The methods of the present invention are especially advantageous for theprocessing of electronic devices.

In addition, the present invention is concerned with structurescontaining electrical conductive patterns on a halogenated polymericcontaining layer.

2. Background Art

Halogenated polymeric materials such as poly(tetra-fluoroethylene)(PTFE) and poly(trifluoromonochloroethylene) are attractive candidatesfor advanced electronic packaging applications because of their very lowdielectric constants, excellent chemical stability, low solvent/moistureabsorption and excellent thermal stability. In addition, certaincomposite halogenated polymer compositions employing composite PTFEmaterials using fillers such as glass or ceramic micro-particles haveimproved dimensional stability and a low thermal expansion coefficient(CTE).

For instance, a glass/ceramic filled poly(tetra-fluoroethylene)available under the trade designation R02800™ has a CTE (x-y) value of16 ppm/°C. which is closely matched to the 16.9 ppm/°C. value for coppermetal. This enhances the thermal cycle reliability of the RO2800™/Cuinterface. The use of these materials in high performance packaging ormultilevel structures would provide reduced signal delay and rise times,reduced cross talk at a given impedance, and increased circuit density.A significant enhancement in the reliability of the packaging structureswould be gained because of the low water uptake by the polymer. Thiswould tend to eliminate corrosion problems, hygroscopic expansion, andimproved metal to dielectric adhesion reliability.

However, because of their relative chemical inertness and hydrophobicnature, these halogenated polymeric materials are difficult to processinto electronic packaging structures. The lack of effective processingtechniques has inhibited the exploitation of these materials by theelectronics industry. The low surface energy of these materials givesthe inability to adhere to other surfaces and must be effectivelyovercome to yield desirable metal adhesion for practical electronicpackaging applications.

In the manufacture of printed circuit cards and boards, a dielectricsheet material is employed as the substrate. A conductive circuitpattern is provided on one or both of the major surfaces of thesubstrate. Since the dielectric substrate is non-conductive, in order toplate on the substrate, it must be seeded or catalyzed prior to thedeposition of metal thereon.

Among the more widely employed procedures for catalyzing a substrate isthe use of a stannous chloride sensitizing solution and a palladiumchloride activator to form a layer of metallic palladium particlesthereon. For instance, one method of catalyzing a dielectric substrateis exemplified by U.S. Pat. No. 3,011,920 which includes sensitizing asubstrate by first treating it with a solution of a colloidal metal,activating the treatment with a selective solvent to remove unreactiveregions from the colloids on the sensitized dielectric substrate, andthen electrolessly depositing a metal coating on the sensitizedsubstrate, for example, with copper from a solution of a copper salt anda reducing agent.

Also, as suggested, for example, in U.S. Pat. No. 3,009,608, adielectric substrate can be pretreated by depositing a thin film of a"conductivator" type of metal particle, such as palladium metal, from asemicolloidal solution onto the dielectric substrate to provide aconducting base which permits electroplating with conductive metal onthe conductivated base.

In addition, there have been various suggestions of treating substrateswith certain materials in order to enhance the attachment to thesubstrate of a non-noble metal catalyst. For instance, U.S. Pat. No.4,301,190 suggests a pre-wet treatment of a substrate with an"absorption modifier" to enhance the attachment to the substrate of anon-noble metal catalyst. Certain surfactants, hydrous oxide sols andcertain complexing agents are suggested as "absorption modifiers".

However, the methods of catalyzing, or seeding, various organic polymersubstrates have not been entirely satisfactory and improvement in thedegree of adhesion of the final metal layer to the substrate has beenless than desired.

This is especially true for polyhaloalkylene containing substrates suchas poly(tetrafluoroethylene) (PTFE), and in fact, the lack of effectiveprocessing techniques has inhibited the effective use of these polymericmaterials by the electronics industry. The hydrophobic nature and lowenergy of the surfaces of poly(haloalkylene) polymers render such quitedifficult to metallize or bond to metal layers normally resulting inpoor adhesion of metal layers to the surface.

It has been suggested, for example, in British Patent 793,731 andfurther suggested, for example, by A. A. Benderly, J. Appl. PolymerScience, 6, 221 (1962), to treat PTFE with very strong reducing speciessuch as elemental alkali metals such as sodium in liquid ammonia orsodium-naphthalene in tetrahydrofuran solutions in order to increase thesurface energy of the surface and render such "wettable" to improveadhesive bonding to metals, plastics, wood and glass.

The use of alkali metal in liquid ammonia solutions has been used totreat PTFE films for improving the adhesion for pressure-sensitive tapeapplications such as suggested by Fields in U.S. Pat. No. 2,946,710.Methods of "activating" perfluorocarbon polymer surfaces for improvedbonding towards organic adhesive coatings by treating with alkalimetals, magnesium and zinc at elevated temperatures in amine solvents orammonia has been reported by Purvis et al. in U.S. Pat. No. 2,789,063.Rappaport in U.S. Pat. No. 2,809,130 suggests methods for improvingbonding between fluorinated resins and other materials by treatingsurfaces with an alkali metal polyaryl hydrocarbon-solvent solution.However, none of these prior art suggestions involves using subsequentin situ reduction of a chemical modification of the fluoropolymersurface for use as a catalyst for subsequent deposition of seed metal.Dousek et al., Electrochimica Acta, 18, 1 (1975), discussed the use ofalkali metals and alkali amalgams to treat PTFE which leads to ahydrophilic "carbonaceous" surface. Because alkali metals reactexplosively upon contact with water liberating hydrogen gas thesesystems are extremely dangerous. Commercially available sodiumnaphthalide solutions such as TetraEtch® (W. L. Gore and Associates) areethylene glycol dimethyl ether solutions such as monoglyme have very lowflash points (e.g. 34° F.) and react violently with water. The highlyreactive nature of alkali metal-liquid ammonia and sodium naphthalidesolutions along with the large capital cost required for safety anddangers associated with handling the raw reagents and waste effluentmake these treatments prohibitive under industrial safety regulations.

Accordingly, the safety controls and concerns that are necessary forsuch a process along with the high equipment costs involved render suchtechniques highly unattractive from a manufacturing viewpoint.

Alternative vacuum or plasma treatment processes have the disadvantagesof requiring high cost vacuum equipment and have a low throughputcapability. Furthermore, such treatments are limited to altering onlythe outermost few atomic layers of the surface and the resulting surfacemodification are unstable and undergo additional changes within hours.As described in, for instance, U.S. Pat. No. 3,689,991 and Tummala, etal. "Microelectronics Packaging Handbook", pp. 409-435, Van NostrandReinhold, flexible polymeric films can be used as carriers in thepackaging of semiconductor chips such as in the so-called TAB (TapeAutomated Bonding) procedure. To date, the primary polymeric materialemployed for such has been polyimide.

One procedure used for employing polyimide as the dielectric and/orcircuit carrier for flexible circuits involves spray coating or rollercoating polyamic acid onto a sheet of metal (such as stainless steel oraluminum). The film is then cured or imidized, resulting in a film whichis fully or substantially fully cured. The metal which the polyimide ison can be imaged, removed, or maintained. On top of the polyimide, threelayers of metal are deposited such as by either evaporation orsputtering. The conductors are chromium or nickel, followed by a layerof copper, followed by a layer of chromium or nickel. By means ofphotolithographic operations, this metal is imaged into circuits.Depending on the use of the circuit, the cured polyimide may or may notbe imaged, either before or after the formation of the circuit.

Flexible circuits have also been fabricated using free-standingpolymeric films such as polyimides onto which metal layers are vacuumdeposited, laminated, or glued. The metal circuit pattern is defined byusing a photoresist pattern to either act as a plating mask or act as amask for subtractive etching of the metal layer. Through-holes in thepolymer film can be made by drilling, punching, or etching.

In a number of these situations, it is necessary to form vias in thepolymeric layer to allow for electrical connections to be made betweenthe different layers of metallurgy. In order that the interconnection beas accurate as possible, it is necessary that the polymeric films resistdistortion of the desired pattern and withstand attack from other wetprocessing chemicals.

For instance, in the formation of multi-layer substrates for mountingchips it is necessary to electrically contact some of the conductors inthe upper or second layer of metallization to some of the conductors onthe lower or first layer of metallization. In order to do so, thepolymeric layer must be selectively etched to form the desired viastherein to allow for metal connection between the upper and lower levelsof metallization and connection to a chip and/or board.

In TAB structures certain regions (windows) must be etched in thepolymer layer in order to expose metal bonding leads such as the innerand outer leads to allow both chip attachment to the TAB package and TABpackage attachment to a circuit card. Caustic solutions are commonlyused to fabricate such windows in TAB structures containing polyimide asthe dielectric.

Conventional electronic packages have conductors comprised of definedmetal regions and might have surface mounted capacitors and resistorsattached. The direct conversion of certain regions of the dielectric toa conductive material would allow fabrication of planar electroniccomponents (i.e., resistors) to be directly fabricated on the dielectricsurface without requiring extra components to be attached.

Wet etching of various poly(halogenated) olefinic polymers such aspoly(tetrafluoroethylene) on a commercial basis has been carried outemploying alkali metals, such as sodium naphthalide or liquid ammoniasolutions. However, such processes suffer from the disadvantagesdiscussed above.

SUMMARY OF INVENTION

The present invention provides methods for treating halogenatedpolymeric materials in order to render them suitable for subsequentplating thereon including metals from an electroless plating bath.Moreover, the present invention provides for enhanced adhesion of themetal to the polymeric material. A further aspect of the presentinvention is concerned with rendering these halogenated polymericmaterials readily etchable in suitable solvents to thereby provideetching processes that are relatively easy to control and do not requirehazardous chemicals. The present invention also provides a method forcrosslinking the halogenated polymeric material.

The present invention affords process simplification, improved chemicalsafety and cost advantages over other metallization methods includinglamination and metal sputtering, or conventional Pd sensitization and,Sn/Pd colloidal surface seeding with electroless plating. Moreover, thepresent invention makes it possible to provide for direct metallizationwith good adhesion and without requiring the use of an adhesive orsurface coating. Also, the present invention makes possible themetallization of two sides, through-holes and irregular surface featuresand is applicable to full-additive metallization schemes by allowingselective and patterned seeding.

In particular, according to one aspect of the present invention, amethod for preparing a halogenated polymeric material-containingsubstrate for subsequent plating of a conductive metal thereon isprovided. The process comprises contacting at least portions of at leastone major surface of said substrate with a reducing agent. Thistreatment results in a chemical modification of the halogenatedpolymeric material surface and reduction thereof such that when thetreated surface is then contacted with a composition containing a metalconstituent wherein the metal is in the positive oxidation state such ascations of a metal or a metal complex in a solution, portions of thesubstrate that were contacted with the reducing agent will be reduced tometal in the zero-valent state. The metal in the zero-valent statethereby provides seed or catalytic sites for subsequent conductivemetallic plating thereon including that from an electroless platingbath.

Another aspect of the present invention is concerned with providing apatterned metallic layer on a halogenated polymeric material-containingsubstrate. The process comprises contacting at least portions of atleast one major surface of said substrate with a reducing agent. Thesaid substrate surface contains a patterned layer of polymer,photoresist or mask which does not react with the reducing agent orprocess solvents permitting only contact of the said substrate andreducing agent at uncoated areas of said substrate. The substrate isthen contacted with a composition containing a metal constituent whereinthe metal is in the positive oxidation state such as containing cationsof a metal or a metal complex which at portions of the substrate thatwere contacted with the reducing agent will be reduced to metal in thezero-valent state. The metal in the zero-valent state thereby providesseed or catalytic sites for subsequent conductive metallic platingthereon including that from an electroless plating bath.

A further aspect of the present invention is concerned with providing ametallic layer on a halogenated polymeric-material-containing substrate.The process includes contacting at least portions of at least one majorsurface of said substrate with a reducing agent; and contacting thesubstrate with an electroless plating bath to thereby provide a metalliclayer at portions of the substrate contacted with the reducing agent.

Another aspect of the present invention is concerned with catalyzingwalls of a via in a halogenated polymeric material-containing substratefor subsequent plating therein of a conductive metal. The processcomprises contacting said substrate with an electrolyte; andcathodically biasing a means for forming said via to therebyelectrochemically reduce said walls of said vial The via walls are thencontacted with a composition containing a metal constituent wherein themetal is in the positive oxidation state such as cations of a metal ormetal complex which will be reduced to metal in the zero-valent state.The metal in the zero-valent state thereby provides seed or catalyticsites for subsequent conductive metallic plating thereon including thatfrom an electroless plating bath.

A still further aspect of the present invention is concerned withplating walls of a via in a halogenated polymeric-containing substratewith an electrically conductive metal. This process includes contactingthe substrate with an electrolyte; cathodically biasing a means forforming said via to thereby electrochemically reduce the walls of thevia; and contacting the substrate with an electroless plating bath tothereby provide a metallic layer on the walls.

A still further aspect of the present invention is concerned with astructure that comprises a free standing halogenated polymericcontaining-layer; and an electrical conductive pattern on the layer. Apreferred structure involves a conductive pattern that includes aplurality of beam leads at least a part of which extends in cantileveredfashion into an aperture in the halogenated polymeric-containing layer.

Another aspect of the present invention is concerned with formingconductive regions at the surface of a halogenated polymeric material.The process comprises exposing at least portions of the substrate to areducing agent to cause chemical modification of the halogenatedpolymeric material; and then exposing the halogenated polymeric materialto a dopant to thereby induce electrical conductivity in those regionsof the halogenated polymeric material chemically modified by thereducing agent. Doping can be achieved through a chemical orelectrochemical oxidation or reduction process. The conductive materialcan be used as conductive regions for circuitry or used as a base forelectroless or direct electrolytic metal plating.

The present invention is also concerned with forming conductive regionsat the surface of a halogenated polymeric material. The processcomprises obtaining an electrode having disposed thereon a halogenatedpolymeric material-containing surface;

contacting the halogenated polymeric-containing surface with anelectrolytic solution;

supplying a voltage between the electrode and a cathode to reduce atleast portions of the polymeric material and cause subsequent chemicalmodification (e.g.--dehalogenation);

and then exposing the halogenated polymeric material to a dopant tothereby induce electrical conductivity in regions of chemically modifiedhalogenated polymeric material. Doping can be achieved through achemical or electrochemical oxidation or reduction process.

Another aspect of the present invention is concerned with etching ahalogenated polymeric-containing substrate. The process comprises:exposing at least portions of said substrate to a reducing agent; andthen exposing the substrate to a solvent to thereby dissolve portions ofthe substrate exposed to the reducing agent.

A still further aspect of the present invention is concerned withetching a halogenated polymeric-containing substrate. The processincludes obtaining an electrode having disposed thereon a halogenatedpolymeric material-containing surface; contacting the halogenatedpolymeric-containing surface disposed on said electrolyte solution;supplying a voltage between the electrode and a cathode to reduce atleast portions of the polymeric material; and then exposing thesubstrate to a solvent to thereby dissolve reduced portions of thesubstrate.

Another aspect of the present invention is concerned with supplyingelectrons to at least a portion of at least one major surface of ahalogenated polymeric material in an amount sufficient to remove halogensubstituents of the polymeric material and to crosslink the materialfrom which the halogen substituents have been removed.

SUMMARY OF DRAWINGS

FIG. 1 is IR SPECTRA for untreated PTFE film and PTFE film treatedpursuant to the present invention.

FIG. 2, is UV-Vis SPECTRA for untreatedtetrafluoroethylene-perfluoralkoxy andtetrafluoroethylene-perfluoralkoxy treated pursuant to the presentinvention.

FIG. 3 is UV-Vis SPECTRA of untreatedtetrafluorethylene-hexafluoropropylene andtetrafluorethylene-hexafluoropropylene treated pursuant to the presentinvention.

BEST AND VARIOUS MODES FOR CARRYING OUT THE INVENTION

The halogenated polymeric materials treated pursuant to the presentinvention are well-known and include such commercially availablepoly(halo)ethylene materials often in the form of a film aspoly(tetrafluoroethylene) given by formula --(CF₂ --CF₂)_(n) --,copolymers of tetrafluoroethylene and hexafluoropropylene,polytrifluorochloroethylene, copolymers of tetrafluoroethylene with forexample olefins such as ethylene and propylene; copolymers oftrifluorochioroethylene with for example olefins such as ethylene andpropylene; copolymers of tetrafluoroethylene with polyperfluoroalkoxyresin with general formula of: ##STR1## wherein n and m individually arewhole number integers greater than of equal to 1, and x and y are wholenumber integers greater than or equal to 1; polyvinyl fluoride;polyvinylidene fluoride; polyvinyl chloride; polyvinylidene chloride;and copolymers of poly(tetrafluoro)ethylene andpoly(di-trifluoromethyldioxole difluoro)ethylene having the followinggeneral formula: ##STR2## wherein the preferred mole percent of dioxoleis about 45 to about 95 mole percent dioxole which yield materials havea dielectric constant of less than 2.0.

Furthermore, the polymeric material treated pursuant to the presentinvention can be compounded with conventional ingredients such as fillersuch as glass and ceramics, antioxidants, stabilizers, plasticizers, andother polymeric materials such as polyimide to comprise a blend.

The polymeric material treated can be free standing or provided on asubstrate such as a metal or polyimide film.

Such commercially available halogenated polymeric materials treatedpursuant to the present invention include those available under thetrade designations. TEFLON (DuPont registered trademark) which includepolymers of tetrafluoroethylene, including TEFLON®DFEp (fluorinatedethylene-propylene copolymers); TEFLON®PFA(copolyperfluoroalkoxy-tetrafluoroethylene); TEFZEL® (copolymer oftetrafluoroethylene and ethylene); available from Allied-SignalCorporation are ACLAR® 22, 88, 33 fluoropolymer films (copolymers andterpolymer consisting primarily of chlorotrifluoroethylene) and; HALAR®(copolymer of chlorotrifluoroethylene and ethylene); KYNAR® 500(poly(vinylidene fluoride)) available from Pennwalt Corporation; KEL-F®(polymer of chlorotrifluoroethylene); HBF-430 (polymer ofchlorotrifluoroethylene); available from Rogers Corporation are RO2800™(poly(tetrafluoroethylene)) filled with glass and ceramic particlesnominally 57% by weight); RO2500™ (poly(tetrafluoroethylene)) filledwith glass particles nominally 11% filler by weight); and RO2510™(composed of Teflon® PFA having nominally 11% filler by weight) andKapton® Type F and Type FN (polyimide coated with fluorinatedethylene-propylene copolymer) available from DuPont; Upilex® C compositefilm derived by coating or laminating Upilex® R polyimide film with FEPfluorocarbon resin from Ube Industries, Ltd., and distributed by ICIAmericas, Inc.; Apical® AF (polyimide films coated with FEPfluoropolymer) from Allied-Signal Corporation; and DuPont Teflon® AF(copolymer of poly(tetrafluoro)ethylene andpoly(di-trifluoromethyldioxole difluoro)ethylene) a soluble,spin-coatable material available as AF1600® and AF2400®.

The reducing agents can be reducing agents or be a compound having astrong electron donating power, per se, or produced such as in situ byelectrochemical means. The reducing agents can be generated by chemicalreaction such as by reacting benzoin and potassium tert-butoxide togenerate an anionic species or by reacting alkali metal (such as Li, Na,K, Rb or Cs) with an aromatic compound such as benzophenone oranthracene to generate an anion species or alkali metal complex of thearomatic compound.

Examples of suitable organic compounds that can be electrochemicallyreduced in an electrolyte solution to provide the chemical reducingagent include, but are not limited to, the following groups ofcompounds: unsaturated aromatic hydrocarbons (e.g., anthracene9,10-diphenylanthracene, naphthalene), aldehydes and ketones (e.g.,benzophenone, benzaldehyde, acetophenone, dibenzoylmethane), imides(e.g., N-n-butylphthalimide, N,N'-di-n-butyl-3,3',4,4'-biphenyltetracarboxylic diimide), nitriles (e.g., α-naphthonitrile,phthalonitrile), carbodiimides (e.g., bis-(p-chlorophenyl carbodiimide),aromatic heterocyclic nitrogen compounds (e.g., 9,10-diazaphenanthrene,quinoline, quinoxaline, phenanthridine), anhydrides (e.g.,1,8-naphthalic anhydride, 3,3',4,4'-benzophenone tetracarboxylicdianhydride), quaternary aromatic nitrogen compounds (e.g.,1-ethylpyridinium bromide), azomethines (e.g., N-p-biphenylbenzalimine),immonium salts (e.g., N-ethyl-N-methyl benzophenone immonium salt), azocompounds (e.g., 4,4'-azobiphenyl), amine oxides (e.g., acridineN-oxide), and organometallic compounds (e.g., dibiphenylchromium (I)iodide, or ruthenium (trisbipyridyl)diperchlorate).

Benzophenone, anthracene, phthalonitrile, flouranthene, phenylacetylene,dibenzanthracene, benzopyrene, phenanthrene, dibenzofuluene,phenylhexatriene, fluorene, naphthacene, naphthalene, perylene andtrans-stilbene are examples of specific compounds that can be reduced toprovide the chemical reducing agents suitable for carrying out thepresent invention. The compounds can be reduced by applying such to anelectrochemical cell containing an anode and a cathode, separatecompartments for anode and cathode, an inert electrolyte solution, andthen applying a bias, voltage, or current.

The compounds can be reduced electrochemically or by bulk electrolysis.Typically, this is done using a two-compartment cell whereby thecompartments are separated by a sintered glass disk or frit having aporosity of less than about 50 μm, preferably less than 10 μm. A saltbridge or semi-permeable membrane, film, or ion exchange material alsocould be used to separate the compartments. The working compartment ishoused with a cathode electrode which is comprised of a metal such asplatinum, mercury, or stainless steel. The anode electrode is comprisedof a conductor such as platinum, carbon, or stainless steel. Forpotentiostatic operation, an appropriate reference electrode ispositioned in the working compartment (e.g., Ag/0.1M Ag NO₃). The cellcan be purged with an inert gas such as nitrogen or argon using an inlettube and one-way valve or bubbler, or operation can be done in a glovebox under an inert atmosphere.

Electrochemical generation of the reducing agent is accomplished byeither galvanostatic, potentiostatic, or voltage-controlledelectrolysis. Typically, the current density range for galvanostaticreduction is 0.1 to 10 mA/cm². In potentiostatic mode, reduction istypically done by applying a potential to the cathode which is morenegative (e.g., 50 mV or more) than the reduction potential for theorganic compounds as measured against the same reference electrode.

For example, the bulk electrolysis to form the active reducing agentsuch as an anionic form of an aromatic organic compound in solution canbe accomplished by potentiostatic operation using a three-electrodearrangement as described hereinabove. In this mode of operation, thereducing power or redox potential of the reducing agent solution can becontrolled and continuously maintained throughout processing since areference electrode is employed. This greatly facilitates processingusing reducing agent solutions and provides reproducible solutionconditions. In addition, electrochemical generation of reduced aromaticorganic compounds has the advantage in that the reactive reduced form ofthese materials is generated on demand and does not require the storageof the reduced solution. Furthermore, the benefits of electrochemicalcontrol can be extended for use with reducing solutions comprised of thereaction between alkali metals and aromatic organic compounds byallowing electrochemical maintenance of the reducing power of thesolution as the active reducing agent becomes oxidized without the needfor adding additional alkali metal. This latter case requires that thepresence of a supporting electrolyte so as to render the solutionsufficiently conductive to support the electrochemistry.

Compounds such as potassium tert-butoxide can react with aromaticketones and alcohols to form anionic species which can act as electrontransfer (reducing) agents. For instance, potassium tert-butoxide reactswith benzoin to form the benzoin dianion.

The reducing agents are preferably generated in an aprotic solvent.

Reaction of solid alkali metals such as lithium, sodium, potassium,rubidium, and cesium with aromatic hydrocarbon compounds in solventssuch as ethers including, tetrahydrofuran, dimethyl ether, dimethylglycol ether and amine solvents such as ammonia, ethylenediamine,hexamethylphosphoramide and morpholine leads to the formation of thecorresponding alkali metal-aromatic compound anion in which the reducedaromatic compound can now act as a reducing agent. The formation of thealkali metal-aromatic compound anion complex is preferred in ethersolvents which facilitates subsequent isolation of the solid form of thealkali metal-aromatic compound anion complex through a chemicalseparation method such as precipitation, filtration, or evaporation. Thesolid anion complex can be redissolved and used in low-volatilitysolvents for better safety and manufacturing.

The synthesis of a reducing agent in an electrolyte solution can becarried out by electrochemical reduction at a cathode electrode surface.The electroreduction can be done using a potential control(potentiostat) or current control (galvanostat) mode of operation.Electrochemical reduction at a cathode electrode requires anelectrochemical oxidation at an anode surface. One type ofelectrochemical cell configuration is the "two-compartment"configuration. In this arrangement, there is a cathode compartment andan anode compartment which are separated by a charge permeable membrane.This membrane prevents bulk mixing of the cathode compartment solutioncontaining electrolytc (cathelyte) and the anode compartment solutioncontaining electrolyte (anolyte) while permitting ion transport to somedegree. The membrane or separator also inhibits contact of the cathodeproducts and anode products. The "two-compartment" configuration can bearranged in a thin layer format allowing continuous flow-throughoperation. During sustained electrolysis, replenishment of the catholyteand anolyte might be necessary to prevent contamination and highelectrolytic solution resistance. The generation of reducing agent inthis system results in the accumulation of reduced species (e.g.,radical-anions) in the cathode compartment. For electroneutralityrequirements, as reduction occurs, cations species supplied by the anodecompartment transport across the membrane.

An alternative cell configuration is the "one-compartment" configurationin which the cathode electrode and anode electrode reside in the samecompartment and share the same electrotyle solution. This cell systemcan be run in similar control modes as discussed for the"two-compartment" configuration. In this arrangement, the cathode andanode products are free to mix and react. Therefore, reduced speciesgenerated at the cathode are free to react with oxidized species at theanode. Alternatively, the product at the electrodes can be gaseousproducts resulting in a change in ionic concentrations at the respectiveelectrodes. Furthermore, the reaction at the electrode can be adeposition reaction resulting in product buildup such as electroplatingor polymer deposition. Furthermore, the reaction at the anode can be adissolution reaction such as in corrosion or etching resulting in theproduction of reactions. In the case of electroreducing to form areducing agent, this mede would result in formation of cations by anodedissolution to act as counter cations for reaction or stabilization ofthe reducing species. For example, reduction of an organic aromaticspecies at a cathode electrode can be accomplished by using a lithium,aluminum, magnesium, or zinc anode which would generate cations as thecounter ion for the anion. This eliminates the need for a separatormembrane and individual control of the catholyte and anolyteelectrolytes.

The preferred aromatic organic compounds are those which when in areduced form (by reacting with an alkali metal) have a reducingpotential in the range of -2.3 V (vs. saturated calomel electrode SCEreference potential, to which all potentials herein are referred unlessotherwise stated) to -1.5 V, with a preferred range of -2.1 to -1.6 Vand a most preferred range between -2.0 and -1.8 V.

The reducing potential ranges for aromatic organic anions are preferredto be more positive than the potentials where solvent reduction beginsfor commonly used non-aqueous, aprotic, polar solvents. It is preferredthat the solvent be of a non-hazardous nature, have a high flashpoint,and have low volatility.

Examples of organic compounds which can be used include polyarylcompounds (e.g., anthracene, 9,10-diphenylanthracene) and aromaticcarbonyl-containing compounds (e.g., benzophenone), aromaticnitriles.(e.g., naphthonitrile, phthalonitrile) and aromaticheterocyclic nitrogen compounds (e.g., phenanthridine). The preferredanionic form of the reacted compound is the one-electron reduced,radical-anion state because generally, they are less susceptible todecomposition and side reactions as compared to the multi-anion statessuch as the dianion or trianion forms.

The organic compound is typically added to the solvent in an amount togive a final concentration of about 0.01 to about 2 Molar, with thepreferred concentration range of about 0.1 to about 1.2M.

A metal such as an alkali metal such as Li, Na, K, Rb, Cs; and alkalineearth metal (Be, Mg, Ca, Sr, Ba, Ra), a group 3B element (Sc, Y, La),and a lanthanum series element (Ce, Pr, Nd, Eu) is added to the organiccompound/solvent mixture in an amount preferably not to exceed theorganic compound concentration. The reaction mixture is most stable whenmaintained under a O₂ -free and H₂ O-free inert (N₂ or Ar) gasatmosphere. Upon addition of the alkali metal, typically, a highlycolored (usually blue) reaction product can be seen streaming from themetal surface within about 30 seconds after addition. The preferredmetal being an alkali metal with the most preferred being K and Na.

Although the alkali metal cation is the preferred cation of the organiccompound anion complex, other cations can be used or exchanged for thealkali metal such as tetraalkylammonium cation, mixed alkyl-arylammonium cation, ammonium cation, phosphonium compound cations,quaternary ammonium cations, chelated or complexed metal cations, orother metal ions as described above. These cations can be introduced byion exchange processes.

Although, these solutions could be used directly in the processes of thepresent invention, as mentioned above, the alkali metal-organic compoundanion complex obtained from the above reaction can be isolated from thereaction solvent to obtain the complex in a solid or crystalline form.The solid complex can be isolated through various techniques whichinclude rotary evaporation, vacuum distillation, or precipitation byusing a non-solvent or solution chilling. Once the solid product isisolated, it should be stored under an O₂ -free and H₂ O-free inert gasatmosphere to achieve maximum stability of the complex.

The solid alkali metal-organic compound anion complex can be addeddirectly to a given processing solvent such N-methyl-2-pyrrolidone toinstantly generate a reducing bath for treating the polymeric materials.The complex should be added to the process solution which preferably hasbeen prepurged to remove oxygen and water, and is maintained under aninert gas blanket. The inert gas blanket should be maintained over thereducing bath to achieve maximum useful bath lifetime. Highlyconcentrated reducing agent solutions can be made in this way.Additional solid complex can be continually added to the processsolution to maintain the desired reducing power. The alkalimetal-organic compound anion complex solution can also contain an inertsupporting electrolyte salt to ensure that the solution is conductiveand facilitate the treatment pursuant to the present invention. Theelectrolyte salt can contain a cation such as an alkylammonium,alkylphosphonium, or alkali metal and also contains an anion such as ahalide, tetrafluoroborate, hexafluorophosphate, perchlorate, or arylsulfonate ion. This supporting electrolyte is desirable if electrolysismethods such as electrochemical reduction is employed for in situregeneration of the reducing agent or monitoring functions.

The alkali metal complexes of anthracene, 9,10-diphenylanthracene, andbenzophenone are the preferred complexes.

The aprotic solvents suitable for use in this invention include, but arenot limited to, the following: nitrile and nitro compounds (e.g.,acetonitrile, benzonitrile, nitromethane), amide and cyclic amidecompounds (e.g., N,N-dimethylformamide, N-methylformamide,N,N-diethylformamide, N-ethylformamide, N,N-dimethylacetamide,N-methyl-2-pyrrolidone, hexamethylphosphoramide), esters, cyclic esters,and ether compounds (e.g., propylene carbonate, ethylene carbonate,γ-butyrolactone, ethyl acetate, tetrahydrofuran, dimethylether), oxideand sulfo compounds (e.g., dimethylsulfoxide, acetone, liquid. sulfurdioxide, sulfolane, dimethylsulfone). The most preferred solvents areN-methylpyrrolidone, N,N-dimethylformamide, and propylene carbonate.

The halogenated material is exposed to the reducing agent usually fromabout 0.1 to about 30 minutes depending upon the desired degree ofreduction of the polymer. The preferred exposure time is about 0.5 toabout 3 minutes. The exposure to the reducing agent results indehalogenation of the polymer structure to leave a carbon-rich surfacesuch as forming carbon-carbon unsaturation, carbon-hydrogen bonds, andgroups such as polyacetylenic units, and providing a higher surfaceenergy and more hydrophilic surface. Certain groups formed by thereduction process can undergo electrochemical or chemical reduction toform anionic species which can then act as reducing species.

Attenuated total reflectance Fourier transform infrared (ATR-FTIR)analysis using an IBM Instruments IR-44, with a liquid nitrogen cooledHgCdTe detector and KRS-5 (thallium bromiodide internal reflectanceelement was done on the following materials: polytetrafluoro-ethylene,copolytetrafluoroethylene-perfluoroalkoxy, polyfluorinatedethylene-propylene, copolyethylene-tetrafluoroethylene,polychlorotrifluoroethylene, and ceramic and glass filled fluoropolymerfilms. Exposing these fluoropolymer films to a solution ofN,N-dimethylformamide (DMF) or N-methyl-2-pyrrolidone (NMP) containing asupporting electrolyte of 0.1M tetrabutylammonium tetrafluoroborate(TBAFB) or 0.1M potassium hexafluorophosphate (KP%) and containing 10 mManthracene which was electrochemically reduced to the correspondingradical-anion form under a nitrogen atmosphere results in the loss ofcarbon-fluorine (C--F) (and chlorine) bonds at the surface and theappearance of new absorbances in the infrared region. For theperfluoropolymers, surface reduction leads to greater loss ofabsorbances at 1203 and 1145 cm⁻¹ (i.e., carbon-fluorine bonds) withlonger exposure to the reduction bath. Concomitant with the C--F loss isthe appearance of new peaks consistent for carbon-hydrogen (C--H) bondsat 2960, 2875, 1472, 1345, and 1059 cm⁻¹ and carbon unsaturation at1635, 1610, and 2100 cm⁻¹ possibly due to carbon-carbon double bonds(alkene units) and acetylenic bonds (alkyne units) as shown by the IRspectra in FIG. 1 for a virgin and anthracene radical-anion treated PTFEfilm. X-ray photoelectron spectroscopic (XPS) analysis of the carbon lsand fluorine ls core level spectra for PTFE films shows that exposingthe PTFE surface to reduced anthracene solutions leads to loss of thefluorine signal and increased carbon signals. Similar XPS data isobtained using different solvents and supporting electrolytes whichindicates that the observed changes in the core-level spectra are notdue to adsorbed or incorporated reactants or solvent and is evidencethat an electrochemical surface reduction and chemical modification hastaken place.

Ultra-violet (UV)/visible (Vis) spectral analysis of differentfluoropolymer films was done using a Hewlett-Packard Model HP 8452Adiode array spectrophotometer to investigate changes in absorbanceproperties of films during reduction and subsequent reactions. Afterimmersing a Teflon® PFA (co-polytetrafluoroethylene-perfluoroalkoxy)film, 2 mils thick, in a DMF solution containing 10 mM anthraceneradical-anion in a nitrogen atmosphere as described above for 10 minutesthe originally visible transparent film has a surface modificationproducing a strong absorbance both in the UV and Vis region whichresults in a gold color, as shown by the spectra in FIG. 2. On exposingthe reduced film to an oxidizing agent (e.g., air) the gold colordisappears leaving a dark brown to black deposit. The visible absorbanceseen for the post-reduced film is lost while the UV absorbance producedduring surface reduction is still present. In addition, exposing areduced fluoropolymer film to a solution containing dissolved metal ions(such as Pd⁺², Ni⁺² Cu⁺¹, Pt⁺², Co⁺², Ag⁺¹) or dissolved metal complexes(e.g. --PdCl₂, PdCl₄ ⁻², Pd(ACN)₂ Cl₂, PdBr₂, PtCl₂, PtBr₂, CuIP(OCH₃)₃,CuBF₄, CoCl₂, NiBr₂, PdSO₄, AgBF₄) results in the loss of visibleabsorbance with concomitant deposition of the metal (Pd, Ni, Cu, Pt, Co,Ag) to its zero-valent state at the modified surface layer. The presenceof such metal deposits is evidenced by the fact that such surfaces arereadily active towards electroless metal plating solution. Similarchanges in the UV-Vis spectra and process behavior are observed forreduction and oxidation of Teflon FEP(co-polytetrafluoroethylene-hexafluoropropylene) films as shown in FIG.3. These results suggest that the reductive treatment of the polymersurface leads to an irreversible chemical modification of the polymerstructure which has a UV absorbance and also produces a reversiblereduced state the modified layer which can be subsequently oxidized.

It is possible that such surface reduction treatment results inelectrochemical defluorination which then leads to the formation ofcarbon unsaturation in the generation of polyenes, polyacetylene, andpolycyclic aromatic groups. Scheme I gives possible reaction sequencesfor polymer reduction and modification. It is likely that such chemicalgroups can undergo further electrochemical reduction by the reducingagents which can initiate electro-defluorination. The visible absorbanceof the reduced films is attributed to anionic forms of the chemicalgroups of the modified surface. ##STR3## where X⁺ is a cationic species

The energetics of fluoropolymer surface and fluorocarbon compoundreduction/modification was investigated using electrochemicaltechniques. The minimum potential required for direct electrochemicalsurface reduction observed as a surface discoloration on contacting aPTFE surface with a stainless steel cathode in a DMF electrolytesolution was -1.79 V vs SCE. Cyclic voltammetry of the fluorinated modelcompound, 2,2,3,3,4,4,4,-heptafluorobutanol (HFBuOH), in DMF gives anonset for reduction at about -1.5 V vs. SCE. No anodic waves areexhibited on positive-going sweeps indicating an irreversible reductionprocess. The proposed mechanism for HFBuOH reduction is electrontransfer leading to elimination of F⁻ ion and formation of HFBuOHradical proceeded by further reduction/elimination. This electrochemicaldata is in agreement with the ability for reducing agents withsufficiently negative oxidation potentials to lead to PTFE surfacereduction. For example, anthracene radical-anion (E⁰ =-1.9 V vs SCE) ismore effective in reducing fluoropolymers compared to benzophenoneradical-anion (E⁰ =-1.7 V), while benzil radical-anion (E⁰ =-1.0 V) iscompletely ineffective. These results are consistent with thosepotentials measured for other halogenated compounds in solution asdiscussed by Ajami in U.S. Pat. No. 4,707,230.

The electrochemical reduction treatment of a PTFE surface as describedabove leaves the modified surface in a reduced form capable oftransferring electrons to a metal constituent wherein the metal is inthe positive oxidation state such as metal ions or metal complexes insolution resulting in metal deposition at the polymer surface. Thisredox-mediated metal deposition process is self-limited and controlledby the amount of charge in the modified surface layer and typicallyleads to a diffuse (electrically noncontinuous) metal deposit. Thedeposition of catalytic metal particles such as Pd, Pt or Cu renders thesurface active towards conventional electroless plating solutions fordepositing a continuous metal layer. Additional electroless orelectrolytic plating can be used subsequently to buildup metal forcircuitization.

Surface modification and electroless metallization by this processresults in strong and reliable metal adhesion. Peel test results showthat cohesive failure occurs in the substrate bulk at a depth well belowthe modified surface layer. Depending on the fluoropolymer material,adhesion values from 2 to 5 lbs./inch for a 1 mil thick plated Cu can berealized. The metal/polymer interface exhibits minimal degradation after1000 hours under 85° C., 81% relative humidity conditions and survivesother packaging reliability tests such as solder shock tests for via PTHintegrity. The process has been successfully used to seed forelectroless plating very high aspect ratio (19:1) plated through holeswith 18 mil diameter. This new process meets the stringent requirementsfor metallization of perfluoropolymer materials for electronic packagingapplications.

The halogenated polymeric material after being reduced by the reducingagent to give chemical modification and anionic surface species can thenbe exposed to a solution containing a metal constituent wherein themetal is in the positive oxidation state such as metal ions or metalcomplexes which are subsequently reduced and deposited at the surfacewhich can then function as the metallic sites or seeds for subsequentmetallic plating.

In particular, the metal ion-containing solution can contain a cation orcomplex of the desired metal such as palladium, platinum, silver, gold,copper, cobalt, and nickel introduced as a metal salt which will contactthe reduced portions of the polymeric material. The reduced portions ofthe surface will thereby transfer electrons to the cation or complex toreduce it to metal atoms in the zero-valent state.

The amount of metal and the depth of metal deposited at the surface isaffected by the degree of chemical modification of the polymer andconcentration of available anions for metal reduction. The metal depositcan be continuous or individual particles comprised of many metal atoms,such particles being diffusely distributed within the region near thechemically modified surface.

The method of the present invention has advantages over conventionalwet, immersion or colloidal Pd seeding techniques. The deposition ofdiffuse seeds in a region near the chemically altered polymer surfaceprovides mechanical interlocking between the subsequent electrolessmetal deposit and the polymer chains to yield increased metal adhesion.The use of strong reducing agents in these aprotic solvents in thereducing composition results in chemical alteration of the polymer and asurface roughening affect. This affect in combination with the seeddeposited diffusely within the converted surface region enhances thesurface adhesion. The increased hydrophilicity improves wetting of themetal deposition solution leading to greater surface area contactbetween the metal and modified surface enhancing mechanicalinterlocking. Furthermore, the formation of new chemical entities at thesurface such as carbon-carbon unsaturation provides possible sites formetal bonding or chemical infraction which might provide improved metaladhesion.

According to preferred aspects of the present invention, both thereducing agent compositions and metal ion seed compositions are employedunder oxygen-free and aprotic conditions since the reducing agent andreduced surface are susceptible to oxidation and hydrogenationreactions. The operations of this invention can be done at anytemperature convenient for use with the compositions under an inertatmosphere, such as a blanket of nitrogen, argon, neon, helium, orhydrogen, the preferred being room temperature and nitrogen.

A preferred seeding or catalyst composition contains about 0.0001-0.05MPalladium-containing complex such as PdCl₂ or PdBr₂ and the seeding isusually accomplished within about 5 minutes. Such compositions areadvantageous as compared to the common colloidal Pd/Sn seed compositionssince such are stable and not subject to autocatalytic decompositioncommon to colloidal Pd seed systems. The palladium deposit so formed isprimarily in the zero-valent state and as such is directly activetowards conventional electroless plating solutions and does not requireactivation or acceleration treatments.

However, the chemical surface treatment by a reducing solution aspursuant to this invention can be applied to modify a fluoropolymercontaining substration for subsequent conventional Pd seeding or Pd/Sncolloid seeding for electroless metallization with the advantage ofimproved metal adhesion and reliability.

If desired, the entire surface of the polymer can be exposed to thereducing agent or only selected portions of the substrate. When apatterned catalyst deposit is desired, selective reduction of portionsof the surface of the polymeric material can be achieved by employingconventional photolithographic techniques prior to contact with thereducing agent. For example, a photoresist can be applied, selectivelyexposed from a pattern and then developed. Examples of suitable negativephotoresists are WAYCOAT SC (J. P. Hunt) and KTFR (Kodak).

This approach permits full-additive (patterned) electrolessmetallization as is desired in the fabrication of multichip modulepackaging and printed circuit devices.

In addition, the surfaces of the polyfluorinated materials can beselectively reduced to provide for patterned metal seed deposition by an"electrowriting" process. The process as will be detailed below employsdirect electrochemical reduction of the surface to irreversibly changethe chemical structure of the polymer surface rendering it hydrophilicand provides improved metal adhesion. The process involves directelectrochemical reduction of the polymer surface by contacting with acathode surface in an electrolyte solution. Selective surfacemodification can be done by directing the electrons to specific portionsof the polymeric surface. Once the region of the surface has beenelectrochemically modified, additional reduction can lead to theformation of anionic species as described above.

The electrons can be supplied to the redox sites of the polymericmaterial also by employing electrochemical means providing the polymeronto a electrode.

A typical arrangement to carry out this particular procedure pursuant tothe present invention is illustrated in U.S. Pat. No. 4,512,855.

The combination of the electrode and polymeric film is then immersedinto an electrolyte solution in an aprotic solvent.

In addition, the composition used to reduce the polymer will include inthe solution an inert supporting electrolyte and preferably a supportingelectrolyte salt that contains as cation a member from one of thefollowing groups: tetraalkylammonium, tetraalkyphosphonium, alkalimetal, aryl-alkylammonium, aryl-alkylphosphonium, or chelated metal. Thepreferred tetraalkylammonium group is tetrabutylammonium, but othertetraalkyls with alkyl group being methyl, ethyl, propyl, isopropyl,pentyl, hexyl, or mixed alkyl thereof-can be employed if desired. Anexample of a typical aryl group is phenyl and an aryl-alkylammonium isbenzyltributylammonium. An example of a chelated metal cation ispotassium 18-crown-6. The supporting electrolyte salt preferablycontains as anion one of the following tetrafluoroborate,hexafluorophosphate, aryl sulfonate, perchlorate, or halide such asbromide or iodide.

The process can be carried out by using a patterned cathode surfaceoperating under potentiostatic, galvanostatic, AC, or DC control. Thecharged cathode electrode can be tailored to a specific surfacestructure including curtain systems, charged flat platens in theelectrolyte solution, patterned platens in solution, flat rollers withcontinuous feed, and patterned rollers with continuous feed.

The rollers can be hydraulically pushed together to insure thatsufficient contact is made to the substrate surface in a manner similarto that used in resist lamination. An additional feature of this methodis that selective surface treatment can be accomplished using a movablecathode "point" electrode to "write" the pattern. This approach involveslocalizing the electron supply.

The rate of surface reduction depends upon the applied voltage orcurrent and the composition of the electrolyte solution. Typically, theapplied cathode potential is in the range of -2.3 V to -1.5 V (vs. SCE),but is preferred to be -2.1 V to -1.8 V (vs. SCE). The applied potentialmust be sufficiently negative as to initiate the reductivedehalogenation reaction.

The electrolyte solution is preferably an aprotic solvent. The aproticsolvents suitable for use in this invention include, but are not limitedto, the following: nitrile and nitro compounds (e.g., acetonitrile,benzonitrile, nitromethane), amide and cyclic amide compounds (e.g.,N,N-dimethylformamide, N-methylformamide, N,N-diethylformamide,N-ethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone,hexamethylphosphoramide), esters, cyclic esters, and ether compounds(e.g., propylene carbonate, ethylene carbonate, γ-butyrolactone, ethylacetate, tetrahydrofuran, dimethylether), oxide and sulfo compounds(e.g., dimethylsulfoxide, acetone, liquid sulfur dioxide, sulfolane,dimethylsulfone).

The halogenated polymeric material after being reduced electrochemicallycan then be exposed to a solution of the metal ion in order to providethe metallic sites or seeds for subsequent metallic plating on themanner discussed above.

Another aspect of the present invention is that through-holes andblind-holes in a substrate can be treated and metallized. The processinvolves forming the through-hole or blind-hole mechanically by, forexample, mechanical drilling or punching.

Pursuant to the present invention, the via formation is carried out withthe polymeric material in contact with, for instance immersed, in anelectrolyte solution. The drill bit or punch head is cathodicallypolarized during the via formation. Typically, the applied cathodicpotential on the via formation item is -2.3 V to -1.5 V (vs. SCE) andshould be sufficiently negative as to initiate electrochemicaldehalogenation which is affected by the particular perhalogenatedmaterial. In this way, as the via is fabricated, contact between thepolymer surface and the metal tool permits direct electrochemicalreduction of the via wall. The electrolyte solutions including thesupporting electrolyte salt as discussed above can be employed toaccomplish the objectives of this aspect of the present invention.

The walls of the vias after being reduced can then be exposed to asolution of the metal ion in order to provide the metallic sites orseeds for subsequent metallic plating in the manner discussed above.

Instead of forming the vias by mechanically drilling or punching, thevias can be formed by employing high current technique to rapidly reduceselected portions of the polymeric material to cause polymer degradationand etching thereof. In particular, a fine "point" electrode is used tolocalize the charge transfer to the area where the via is desired. Thepolymeric material during this is in contact with, for instanceimmersed, in an electrolyte solution. The electrolyte solutionsincluding the supporting electrolyte salt as discussed above can be usedfor this purpose. As dissolution occurs the electrode probe can bedriven into the substrate. The via profile is controlled by theself-limiting etching of the via walls as the electrode probe passes.This process leaves the via wall chemically modified and capable ofbeing catalyzed or seeded.

The potential applied to the "point" electrode must be sufficientlynegative to initiate electrochemical dehalogenation, or at least >-1.5 Vvs. SCE. It is preferred that the applied potential be as negative aspossible but not so negative as to lead to electroreduction of thesolvent or electrolyte. For example in the case of DMF, application ofpotential in the range -2.3 to -2.0 V vs. SCE is preferred.

The walls of the vias after being reduced can then be exposed to asolution of the metal ion in order to provide the metallic sites orseeds for subsequent metallic plating in the manner discussed above.

In addition, according to the present invention, the reduced portions ofthe fluorinated polymeric material can be metallized directly withoutthe need to utilize a separate seed step prior to the metal deposition.

For example, the reduced polymer sites act as the catalyst wherebyelectroless metal plating is initiated by electron transfer from reducedpolymer sites to metal cations in the electroless bath which depositsmetal in situ and permits continued electroless plating due to theoxidation of the reducing agent provided in the electroless platingbath. However, use of the seed provides for more uniform surfaceactivation which in turn gives more uniform electroless metal depositionand enhanced adhesion between the metal and polymer.

In any event, once the desired portions of the halogenated polymer havebeen conditioned to render it susceptible for subsequent deposition of ametal, the polymeric material can be electrolytically plated or exposedto an electroless metal plating bath. Suitable metals include copper,nickel, gold, palladium, cobalt, silver, platinum, tin, or mixturesthereof. The preferred metals are copper, nickel, cobalt and palladium.Suitable copper electroless plating baths and their method ofapplication are disclosed in U.S. Pat. Nos. 3,844,799 and 4,152,467,disclosures of which are incorporated herein by reference, except thatit is preferred to use a low cyanide concentration or exclude thecyanide for purposes of this invention, when forming an initial metalstrike (500 to 10,000 Angstroms).

The copper electroless plating bath is generally an aqueous compositionthat includes a source of cupric ion, a reducing agent, a complexingagent for the cupric ion, and a pH adjuster. Such also usually include acyanide ion source and a surface-active agent. Cyanide ions should beexcluded or controlled to low levels (i.e. --1-4 ppm) when using asurface seeded with Pd metal in accordance with the present inventionsince the cyanide can complex and dissolve the Pd.

The cupric ion source generally used is cupric sulfate or a cupric saltto the complexing agent to be employed.

When employing cupric sulfate, it is usually employed in amounts ofabout 3 to about 15 grams/liter and more usually from about 8 to about12 grams/liter. The most common reducing agent is formaldehyde which isgenerally used in amounts from about 0.7 to about 7 grams/liter and moreusually about 0.7 to about 2.2 grams/liter.

Examples of some suitable complexing agents include Rochelle salts.,ethylenediaminetetraacetic acid, the sodium (mono-, di-, tri-, andtetra-sodium) salts of ethylenediaminetetraacetic acid,nitrilotetraacetic acid and its alkali salts, gluconic acid, gluconates,triethanolamine, glucono-(gamma)-lactone, and modified ethylenediamineacetates such as N-hydroxyethylethylene-diaminetriacetate. In addition,a number of other suitable cupric complexing agents are suggested inU.S. Pat. Nos. 2,996,408; 3,075,856; 3,075,855; and 2,938,805. Theamount of complexing agents dependent upon the amount of cupric ionspresent in solution is generally from about 20 to about 50 grams/literor in a 3-4 fold molar excess.

The plating bath also usually contains a surfactant that assists inwetting the surface to be coated. A satisfactory surfactant is, forinstance, an organic phosphate ester available under the tradedesignation GAFAC RE-610. Generally, the surfactant is present inamounts from about 0.02 to about 0.03 grams/liter.

Also, the pH of the bath is generally controlled, for instance, by theaddition of a basic compound such as sodium hydroxide or potassiumhydroxide in the desired amount to achieve the desired pH. The pH isusually between about 11.6 and 11.8.

The plating baths generally have a specific gravity within the range of1.060 to 1.080. The temperature of the bath is usually maintainedbetween 70° C. and 80° C. and more usually between 70° C. and 75° C. TheO₂ content of the bath is generally contained between about 2 ppm andabout 4 ppm and more usually about 2.5 ppm to about 3.5 ppm by injectingoxygen and an inert gas into the bath. The overall flow rate into thebath is usually from about 1 to about 20 SCFM per thousand gallons ofbath.

In addition, the polymers in the reduced state obtained in the mannerdisclosed above and especially the polyimides can be readily andselectively etched by dissolving the reduced polymeric material in anaprotic organic solvent.

With respect to that aspect of the present invention concerned withetching the halogenated polymeric materials, the polymeric materials canbe reduced by either direct electrochemical reduction at an electrodesurface or through chemical reduction using a reducing agent in anelectrolyte solution in contact with the polymeric material.

After the desired portions of the polymeric material are reduced, thematerial is contacted with a solvent capable of dissolving or etchingthe reduced portions of the polymeric material. Suitable solvents forthis purpose include aprotic, polar solvents such asN,N-dimethylformamide, N-methyl-2-pyrrolidone, N,N-dimethylacetamide,propylene carbonate, hexamethylphosphoramide, dimethylsulfoxide. Otherreagant systems include sulfuric, nitric, hydrochloric, phosphoric orother strong oxidizing solution which can attack the modified polymerand lead to dissolution.

The reducing pursuant to this aspect of the present invention can becarried out by any of the methods described above using a reducing agentor by electrochemical means. However, the reduction carried out for thepurposes of etching is generally conducted to proceed to a greaterdegree than that for the purposes discussed above. For example, whenemploying an electrochemical technique, surface reduction isaccomplished by contacting the polymeric surface with a conductivesubstrate under cathodic bias in a nonaqueous electrolyte solution.

The electrolyte solutions disclosed above can be used for this purpose.Electrons from the electrode are transferred into the polymer surfaceresulting in defluorination of the polymer structure near the surface atthe contact point. The reduction reaction also leads to the generationof carbon-carbon double bonds and/or acetylenic unsaturated bonds whichthen can disproportionate, cross-link, and form polycyclic aromaticunits. Further reduction of the chemically "modified" surface regionresults in the generation of anionic and radical species and ultimatelyresults in bond scission. This reduction decomposition leads tobreakdown of the polymer chain and the formation of low molecular weightspecies which are soluble.

The portions of the polymeric material that are not reduced are notsoluble in the above solvents. In order to insure that the necessarystage of reduction has been reached to render it etchable, completedehalogenation is first required before etching (i.e., carbon-carbonbond scission) occurs, which under reducing condition will occur firstsince the electroreduction of C--Cl, C--Br, C--F bonds is kineticallyand thermodynamically favored.

Patterned etching of the surface can be done by using a patternedcathode electrode or by scanning an electrode across the surface.

When employing a reducing agent, those areas of the polymeric substratethat are not to be reduced are protected from contact with the reducingagent by a layer of material (e.g. resist or mask) that has beendelineated by conventional lithographic processing. The compositionsused for the reducing are those discussed hereinabove.

A further advantage of the etching carried out pursuant to the presentinvention is that the walls of the patterned impression etched into thesurface would also be modified and left in a reduced form which could bedirectly metallized using the metallization techniques discussed above.

In fact, the metallization can be accomplished directly by employingelectroless metal plating. The metal circuitry built up in the channelswould yield a planar surface structure by having the metal linesembedded in the substrate. This personalization approach also eliminatesthe possibility of current leakage between lines because of the physicalbarrier between conductors.

The etching process of the present invention is advantageous over priorart alkali metal and sodium naphthalene/ether treatment techniques sincethere is no need for highly reactive and explosive chemicals or highlyflammable solvents. The procedure by which reducing agents are generatedelectrochemically has the advantages of allowing direct control of thereduction rate which can be easily monitored during processing, asdiscussed hereinabove. The use of alkali metal-organic compound anioncomplexes in low volatility solvents (e.g. NMP) eliminates the flashpoint concerns associated with ether solvents.

Another aspect of the present invention is concerned with formingconductive regions at the surface of halogenated polymeric materials.The process is essentially advantageous for fabricating surfaceresistors between circuit lines on semiconductor chips on ceramicmodules (CERMET).

The present invention makes it possible to directly fabricate conductingpolymer surface resistors and conductors. The reduction process pursuantto this invention can lead to the transformation of the halopolymer topolyacetylenic or conjugated groups which can be made conductive. Theprocess includes reducing at least portions of the surface of ahalogenated polymeric material and then exposing the halogenatedpolymeric material to a dopant to thereby induce electrical conductivityin reduced regions of the halogenated polymeric material. The reducingpursuant to this aspect of the present invention can be carried out byany of the methods described above of using a reducing agent or byelectrochemical means.

If it is desired to form conductive regions at only portions of thesurface of the halogenated polymeric material, patterned conductivemodified polymeric surface regions can be formed by either selectivesurface reduction using a patterned resist mask or by patterning themodified surface with a resist prior to the doping. Patterned orselective modification of the surface can also be carried outelectrochemically by localizing electron supply to selected portions ofthe surface such as by using a movable cathode "point" electrode to"write" the pattern.

In the case of reductive doping, the modified halopolymer material isreduced and positive ions are incorporated to maintainelectroneutrality, while oxidative doping results in the oxidation ofthe polymer and requires negative ions to balance the charge.

Dopants used to provide the conductivity include reductive or oxidativedoping such as iodine.

Reductive doping can be accomplished through a variety of chemical orelectrochemical means such as exposure to hydrogen or by exposure to areducing solution as those included herein. Oxidative doping can be doneby treating with a sufficiently oxidizing solution (e.g., persulfate) orexposure to iodine vapors. Conductivity imparted by oxidative orreductive doping is obtained by introducing mobile charge carriers(electrons or holes) onto conjugated units of the chemically modifiedperhalopolymer material.

The techniques of the present invention can be advantageously used in awide variety of processes to fabricate various structures some of whichwill be described below.

An integrated circuit board and specifically a circuitized power corelayer can be obtained by the following sequence of fabrication steps. Inparticular, a circuitized power core is obtained by laminating a metallayer, such as copper or copper-invar-copper to a fluorinated polymericsubstrate typically about 1 to about 10 mils thick. The top and bottomsurfaces of the laminate are roughened to facilitate subsequent adhesionsteps by removing the sacrificial copper layer by etching such as usinga ferric chloride or persulfate etchant composition. Next, via holes areprovided and the walls of the vias of the fluorinated polymeric materialreduced according to the techniques discussed hereinabove.

Next, the desired power planes on the outer surfaces of the fluorinatedpolymeric material are etched back, for instance, by employing chemicalwet etching such as a ferric chloride or cupric chloride solution or byan electrochemical-assisted anodic etching process.

For example, electroetching of a Cu core exposed within through holescan be done by applying a constant d.c. voltage of 1.15 V between thecore and some other electrode such as a piece of Cu or Pt foil, wherethe Cu core is made positive with respect to the other electrode. Thesolution used for this etching can be in general any acidic aqueoussolution such as 0.35M H₂ SO₄ or a neutral salt solution such as 0.5Msodium nitrate. The voltage is applied typically for more than 30seconds and maintained until the desired amount of material is removed.

A dielectric layer is then provided over the defined power plane inorder to insulate such by solvent coating, spin casting orelectrophoretic deposition of a dielectric material. A typical procedureemployed can be electrophoretic deposition of a dielectric layer such asphotoresist, epoxy or polyimide layer. Typically, such layer is about0.1 mils thick to about 5 mils thick.

Power plane vias are then provided by the techniques discussed above andthe walls of the vias through the fluorinated polymeric material arereduced by the techniques described hereinabove. The walls of the viasare then provided with a seed or catalytic material such as palladium asdiscussed above.

A pattern is then provided in the insulating layer by employingconventional lithographic techniques such as applying a photoresistmaterial such as KTFR or WAYCOAT SC, negative resist materials. Theresist is then exposed through a suitable mask to actinic light and thendeveloped to provide the desired pattern. The dielectric material isthen removed in the desired locations exposing the underlying metallicmaterial of the power plane. On top of the exposed portion is platedfrom an electroless bath a conductive metal such as copper or nickel andpreferably copper to provide the desired pattern. Next, the remainingphotoresist is stripped from the structure by well-known techniques tothereby provide the desired power core layer.

Another structure is provided by reducing the surface up to about20-1000 Å of a fluorinated polymeric material film of about 0.3 to about5 mils thick and typically about 3 mils thick. The surface layer can bereduced by the techniques discussed above and preferably by contact witha reducing agent. Inner/outer lead windows and fiducial marks are thenprovided in the polymeric substrate such as by punching or excising thefluorinated polymeric material. Fiducial marks are mechanical alignmentholes for continuous feed or roll-to-roll handling in TAB tapeprocessing. A photoresist and preferably a negative photoresist such asKTFR or WAYCOATE is laminated to both sides of the fluorinated polymericsubstrate to a thickness typically of about 0.1 to about 3 mils thick,an example which is about 1 mil thick. The photoresist material is thenexposed to a pattern to actinic light through a mask to thereby providean image within the inner/outer lead window areas. The resist isdeveloped in the inner/outer lead window areas and preferably leaving anoverlap onto the fluorinated polymeric material near the edges of thewindows of about 2 to about 20 mils to insure that the resist is held inplace. Both sides of the fluorinated polymeric film and laminatedphotoresist are then blanket seeded with, for example, palladium by thecatalyzing or seeding procedures discussed above. A metal layer of about500Å to about 0.2 mils thick is then provided over the seed from anelectroless strike bath. A typical example of a suitable copper strikebath contains 15 g/L CuSo₄.5H₂ O; 62 g/L KNa C₄ H₄ O₆.4H₂ O; 22 g/LNaOH; 20 ppm Gafac® surfactant; and 75 75 ml/L HCHO in H₂ O and used atnormal room temperatures. Next, a photoresist layer is laminated ontoboth sides of the substrate followed by selective exposure to actiniclight through a mask to provide the desired circuit pattern. Thephotoresist can be the same or different than the photoresist employedin the prior step of this procedure. The photoresist is developed tothereby opened circuit areas and exposing the plated and seeded areas.Additional metal is then plated up to the desired thickness such as byan electrolytic plating process employing an acidic copper plating bath.A typical bath containing 59 g/L CuSO₄.5H₂ O; 28 ml/L concentrated H₂SO₄ ; 50 ppm HCl; and 10 ml/L Chemcut Corp. additive, and using aplating rate of 10 to 35 mA/cm² employing copper anodes. The resist isthen stripped by etching in a suitable solvent and the layer from thestrike bath is then removed by flash etching such as using an etchingcomposition containing ferric chloride and HCl. The first photoresistlayer can now be stripped. The copper plating is then plated with alayer of gold to facilitate subsequent soldering or other types ofconnections. The substrate can then be cut to provide the desired sizingfor use as a TAB package.

Another procedure to fabricate a structure includes the steps ofreducing about 20-10001 Å of both sides of a fluorinated polymericmaterial film such as Kapton® Type FN which is a polyimide film of about0.5 to 3 mils coated on both sides with a 0.1 or 0.5 mil thickfluorinated ethylenepropylene copolymer. Both surfaces are then blanketseeded and plated with about 500-10,000Å mils thick copper layer from anelectroless strike bath by the techniques discussed above. A photoresistis then laminated to both sides of the surface. The photoresist is thenpatterned by conventional photolithographic techniques by exposurethrough a mask followed by subsequent developing to provide the desiredcircuit pattern. The circuit pattern is then plated to the desiredmetallic thickness such as by an electrolytic plating typical of whichis an acidic copper plating bath as described above.

Next, the remaining photoresist is removed by employing a suitablestripping composition. A second photoresist is then laminated to bothsides of the substrate. The second photoresist is then exposed through amask to actinic light to define the desired inner/outer lead window andthe photoresist is then developed. The metallic layer from the strikebath is then removed by flash etching to thereby leave the window etchmask in place. The inner/outer lead windows are opened by etching thepolymeric material employing a aprotic solvent. The second photoresistis then removed by stripping and the underlying metal layer is removedby flash etching. The copper layers can then be gold plated to enhancetheir ability to be soldered and the structure is sized to desired sizeby cutting.

Another technique to fabricate a structure includes reducing about20-1000Å on each side of a fluorinated polymeric material substrate ofabout 0.3 to about 5 mils thick by the techniques described above. Bothsides of the substrate are then blanket seeded and coated with a metallayer of about 500 to about 10,000 Å thick from an electroless strikebath as described above. A photoresist is then laminated to both sidesof the substrate. The photoresist is patterned to provide desiredcircuit pattern by conventional photolithographic techniques by exposingthe photoresist to actinic light through a mask followed by developingthe photoresist to open the desired circuit areas. Metal is then platedup to the desired thickness in the opened circuit areas by, for example,electrolytic plating. Typical electrolytic bath is an acidic copperplating bath of the type described above. The photoresist is thenstripped and the thin metallic layer from the strike bath is removed bya flash etching. A second photoresist is then laminated to both sides ofthe substrate. This photoresist is patterned to provide the desiredinner/outer lead window areas by conventional photolithographic means.In particular, the second photoresist material is exposed to actiniclight through a mask to define the desired inner/outer lead window areasand then the resist is developed.

The fluorinated polymeric material is then laser ablated from each sideto thereby open the desired windows and leads with, for example, 193 nmwavelength laser. The second photoresist is then stripped and the coppercircuitry is provided with a gold layer. The structure can then be sizedto desired size by cutting.

Another fabrication process comprises coating onto both surfaces of afluorinated polymeric material substrate such as by spin-coating aphotoresist such as KTFR or WAYCOATE SC. The photoresist is thensubjected to conventional photolithographic technique by exposurethrough a mask to actinic light to provide the desired circuit patternfollowed by development of the resist to open the desired circuit areas.Next, the bare surface areas, those not covered by the photoresist, arethen reduced by the techniques described above to a thickness of about20 to about 1000 Å. Seed metal is then deposited at the reduced surfaceareas. The metal circuit pattern is then provided by plating from anelectroless plating bath such as an electroless copper plating bath ofthe type described above. The photoresist is then removed by stripping.

A second photoresist is then laminated to both sides of the substrate.The inner/outer lead window areas are then defined by conventionalphotolithographic techniques such as by exposure through a mask and thendevelopment of the photoresist to provide the desired inner/outer leadwindow areas. The inner/outer lead windows are then opened by removingthe fluorinated polymeric material not protected by the photoresistmaterial such as by wet etching or preferably by laser ablation.

The second photoresist is then stripped and the copper lines are goldplated. The device can then be sized to desired dimensions by cutting.

It is further noted that in any of the above described fabricationtechniques, the reduction of the fluorinated polymeric material can becarried out by direct electrochemical reduction using a patternedelectrode substrate. This eliminates the need for at least one of thephotoresists in order to define the area that will be metallized.However, a subsequent resist pattern may be desired prior to electrolessplating in order to prevent lateral metal buildup which could lead toshorting and limit resolution of the metal lines during plating on aflat surface.

The following non-limiting examples are presented to further illustratethe present invention.

EXAMPLE 1

A one liter solution of N,N-dimethylformamide (DMF) containing 0.05Manthracene and 0.1M tetrabutylammonium tetrafluoroborate (TBAFB) ispurged thoroughly with purified nitrogen gas (having <2 ppm oxygen) orassembled and maintained in a nitrogen glove box is electrochemicallyreduced at a constant current of 70 mA using a platinum mesh cathode(approximately 90 cm area) using a two-compartment cell separated by afritted glass disk (porosity <8 μm) with continuous solution stirring.The average measured cathode potential is -2.1 V vs. saturated calomelelectrode (SCE). During electrolysis the characteristic blue color ofthe anthracene radical-anion generated at the cathode surface diffusesinto the solution. On further reduction the solution darkens and becomesnearly black and opaque. The reduction is discontinued when 15% of theanthracene content is converted to the anthracene radical-anion formresulting in a 7.5 mM anthracene radical-anion concentration.

Six PTFE blocks measuring 10 cm×10 cm×0.5 cm are immersed in theanthracene/DMF reducing agent solution described above for 30 seconds, 1minute, 3 minutes, 5 minutes, 10 minutes, and 30 minutes each. Thistreatment results in discoloration of the PTFE surface and greaterdarkening is observed with increasing exposure time in theanthracene/DMF solution. Rinsing the samples in nitrogen purged DMF hasno affect on the surface color. Deposition of catalytic metal seeds isaccomplished by immersing the reduced samples in a DMF solutioncontaining 5 mM PdCl₂ for 2 minutes. The samples are then rinsed withDMF and dried. The surface exhibits no electrical conductivity. Alloperations to this point are performed under an inert atmosphere. Theoperations which follow are under ambient conditions unless statedotherwise.

An electroless copper plating solution having the following composition:15 g/L CuSO₄.5H₂ O; 62 g/L KNaC₄ H₄ O₆.4H₂ O (Rochelle salt); 22 g/LNaOH; 20 ppm Gafac 610; and 7.5 ml/L HCHO (37%) is prepared withdeionized water. The above treated PTFE samples are immersed for 3minutes in the electroless Cu bath at room temperature. Highlyreflective, continuous Cu metal films are electrolessly deposited ontothe PTFE surfaces.

The copper thickness is increased to 1 mil by electrolytic plating usingan acid copper solution having the following composition: 59 g/LCuSO₄.5H₂ O; 28 ml/L conc. H₂ SO₄ ; 50 ppm HCl; and 10 ml/L surfactantsolution, and plating rate of 20 mA/cm². 30 mil wide polymer decals areapplied to the Cu surface and the sample is then exposed to a FeCl₃ /HCletchant solution to selectively remove any exposed Cu in order to definethe 30 mil wide adhesion peel lines. Peel tests (90°) results giveadhesion values between 2.0±0.5 lbs./inch with cohesive failureoccurring well within the PTFE substrate bulk. A PTFE sample treated for30 minutes in the reducing bath and subsequently metallized with peellines has a time zero adhesion value of 1.8 lbs./inch. After 100 hoursunder 85° C./85% relative humidity conditions, the adhesion increases to2.7 lbs./inch with cohesive failure well within the PTFE substrate bulk.

EXAMPLE 2

An anthracene reducing solution and Pd seeded PTFE substrates areprepared as in Example 1. An electroless nickel plating solution is madeusing 30 g/L NiCl 6H₂ O; 22 g/L Na₃ C₆ H₅ O₇ 2H₂ O (sodium citrate); 50g/L NH₄ Cl; 10 g/L NaH₂ PO₂ ; pH 8.5 and used at 85° C. Exposure of thePd seeded PTFE substrates to this electroless Ni bath for 3 minutesresults in the deposition of highly reflective, electrically conductiveNi films. Electrolytic acid Cu plating is done to increase the metalthickness to 1 mil and peel lines are formed as described in Example 1.Adhesion values measured are similar to those prepared in Example 1 withcohesive failure occurring well within the PTFE substrate bulk.

EXAMPLE 3

A one liter solution of N-methyl-2-pyrrolidone (NMP) containing 0.05Manthracene and 0.1M tetraethylammonium tetrafluoroborate (TEAFB) isprepared and subjected to conditions and electrolysis as described inExample 1. The reductive electrolysis of anthracene is discontinued when15% of the anthracene content is converted to the correspondingradical-anion form to give a 7.5 mM reducing agent concentration.

PTFE blocks measuring 10 cm×10 cm×0.5 cm are immersed in theanthracene/NMP reducing agent solution prepared as above for timesranging between 1 minute and 1 hour, with resulting surfacediscoloration but to a lesser degree as compared with similar exposuretimes in the anthracene/DMF solution as described in Example 1. Rinsingthe samples in nitrogen purged NMP has no affect on the surface color.Deposition of catalytic metal seeds is accomplished by immersing thereduced samples in a NMP solution containing 5 mM PdCl₂ for 2 minutes.The samples are then rinsed with NMP and dried. The surface exhibits noelectrical conductivity. All operations to this point are performedunder an inert atmosphere. The operations which follow are under ambientconditions unless stated otherwise.

An electroless copper plating solution and procedure for depositing acopper film on the PTFE surfaces is as described in Example 1. Immersionfor 3 minutes in the electroless Cu plating bath gives highlyreflective, electrically continuous Cu deposits.

EXAMPLE 4

An anthracene reducing solution and Pd seeded PTFE substrates areprepared as in Example 3. An electroless nickel plating solution isprepared as described in Example 2 and used to deposit highlyreflective, electrically continuous Ni films onto the Pd seeded PTFEsubstrates.

EXAMPLE 5

An anthracene reducing solution is prepared as described in Example 1. Atransparent film of Teflon® PFA measuring 2 cm×10 cm×2 mil thick isimmersed in the anthracene/DMF bath for 5 min and Pd seeded and anelectroless Cu film is deposited as described in Example 1.

EXAMPLE 6

An anthracene reducing solution is prepared as described in Example 1. Atransparent film of Teflon® FEP measuring 2 cm×10 cm×2 mil thick isimmersed in the anthracene/DMF bath for 5 min and Pd seeded and anelectroless Cu film is deposited as described in Example 1.

EXAMPLE 7

An anthracene reducing solution is prepared as described in Example 1. Afilm of HBF-430 (polychlorotrifluorethylene with filler) measuring 2cm×10 cm×2 mil thick is immersed in the anthracene/DMF bath for 3minutes and Pd seeded and an electroless Cu film is deposited asdescribed in Example 1.

EXAMPLE 8

An anthracene/DMF reducing solution is prepared as described inExample 1. Two RO2800™ (PTFE) samples measuring 4 cm×4 cm×5 mils areexposed to the reducing bath for 30 seconds and 30 minutes each to causesurface reduction. The samples are then rinsed with acetonitrile (ACN)and seeded with Pd by subsequent immersion in a solution containing 2.5mM PdCl₂ in ACN for 2 minutes. Rutherford backscattering analysis of aportion of the surface of each sample gives 8.6×10¹⁵ Pd atoms/cm² forthe 3 minutes reduction and 3.5×10¹⁶ Pd atoms/cm² for the 30 minutesreduction. ESCA surface analysis shows significant loss of fluorine andincreased carbon signal which is also more pronounced for the longerexposure. Uniform electroless Cu and Ni deposits are readily formed inan electroless Cu solution as described in Example 1 and uniform Nideposits are formed in an electroless Ni solution as described inExample 2 after 15 minutes plating. The metal thickness is increased byelectrolytic acid Cu plating as described in Example 1. The followingtable lists results of 90° peel testing done using 2 mm wide Cu linestrips defined by selective subetching and subjected to 85° C./85%relative humidity environment.

    ______________________________________                                                                        100   1000                                    REDUCTION ELECTROLESS INITIAL   HOURS HOURS                                   TIME (min)                                                                              METAL       LBS/IN    LBS/IN                                                                              LBS/IN                                  ______________________________________                                        0.5       Cu          3.4       3.8   2.7                                     0.5       Ni          2.5       3.1   2.8                                     5         Cu          1.1       1.6   1. 8                                    ______________________________________                                    

EXAMPLE 9

An anthracene/NMP reducing bath is prepared as described in Example 2.Two R02800™ (PTFE) samples measuring 4 cm×4 cm×5 mils are exposed to thereducing bath for 30 seconds and 30 minutes each to cause surfacereduction. The samples are then rinsed with ACN and seeded with Pd bysubsequent immersion in a solution containing 2.5 mM PdCl₂ in ACN for 2minutes. Rutherford backscattering analysis of a portion of the surfaceof each sample gives 1.1×10¹⁵ Pd atoms/cm² for the 3 minutes reductionand 2.3×10¹⁵ Pd atoms/cm² for the 30 minutes reduction. ESCA surfaceanalysis shows significant loss of fluorine and increased carbon signalwhich is also more pronounced for the longer exposure. The chemicalmodification for the NMP reducing bath occurs to less of an extent ascompared to a similar bath using DMF. Uniform electroless Cu and Nideposits are readily formed in an electroless Cu solution as describedin Example 1 and electroless Ni solution as described in Example 2 after15 minutes plating. The metal thickness is increased by electrolyticacid Cu plating as described in Example 1. The following table listsresults of 90° peel testing done using 2 mm wide Cu line strips definedby selective subetching and subjected to 85° C./85% relative humidityenvironment.

    ______________________________________                                                                        100   1000                                    REDUCTION ELECTROLESS INITIAL   HOURS HOURS                                   TIME (min)                                                                              METAL       LBS/IN    LBS/IN                                                                              LBS/IN                                  ______________________________________                                        0.5       Cu          3.1       3.6   3.3                                     0.5       Ni          2.9       3.0   2.9                                     ______________________________________                                    

EXAMPLE 10

An anthracene solution is prepared as in Example 1 except using insteadof TBAFB, 0.1 M KFP₆ is used as supporting electrolyte. PTFE, PFA,HBF-430, and RO2800 samples are reduced for 5 minutes and Pd seeded asin Example 8. ESCA analysis of a portion of the RO2800 sample is similarto that for samples analyzed in Example 8. Uniform electroless Cu and Nideposits are readily formed on all these substrates in an electroless Cusolution as described in Example 1 and electroless Ni solution asdescribed in Example 2 after 15 minutes plating.

EXAMPLE 11

An anthracene/NMP reducing bath is prepared as described in Example 2.Samples of Kapton® FN measuring 4 cm×4 cm×5 mils is exposed to thereducing bath for 3 minutes to cause surface reduction and results indiscoloration of the surface. The samples are then rinsed with ACN andseeded with Pd by subsequent immersion in a solution containing 2.5 mMPdCl₂ in ACN for 2 minutes. Uniform electroless Cu and Ni deposits arereadily formed in an electroless Cu solution as described in Example 1and electroless Ni solution as described in Example 2.

EXAMPLE 12

RO2800 samples are exposed to an anthracene/NMP reducing bath asdescribed in Example 2 for 5 minutes, then rinsed with ACN and dried at90° C. for 30 minutes in a vacuum oven under ambient conditionsresulting in a textured surface for improving resist adhesion. WaycoatSC liquid photoresist is applied and irradiated through a mask having aVLSI packaging pattern. The resist is developed leaving behind apatterned resist layer having 2 mil wide channels and 4 mil-wide resistregions as a negative of the desired circuit pattern. The resistpatterned substrate is then immersed in the anthracene/NMP reducing bathof this example for 5 minutes, then rinsed with ACN and the exposedmodified RO2800 areas Pd seeded as described in Example 9. Afterseeding, the substrate is thoroughly rinsed for 5 minutes with a streamof methanol and dried before exposing to an electroless Cu solution asdescribed for 10 minutes to deposit a Cu layer onto those areas notcoated with the resist layer. This patterned electroless depositionprocess can also be done by application of an appropriate resist to apreviously untreated fluoropolymer surface.

EXAMPLE 13

A DMF solution containing 0.05M benzophenone and 0.1M TBAFB wassubsequently prepared and electrochemically reduced and maintained asdescribed in Examples 1 and 2. The reductive electrolysis is thendiscontinued after 15% of the benzophenone content was converted to thecorresponding benzophenone radical-anion form to yield a 7.5 mMradical-anion solution. A sample of PTFE, Teflon PFA, and RO2800 areeach immersed for 5 minutes to reduce the substrate surface. Pd seedingis accomplished by subsequent exposure to a solution of 5 mM PdCl₂ inACN, rinsed with ACN and dried in air. Uniform electroless Cu or Nideposits can be formed on these Pd seeded substrates as per previousplating descriptions.

EXAMPLE 14

A sodium anthracene (NaAn) solution is prepared by adding about 3.56 gof anthracene to about 200 ml tetrahydrofuran (THF) under a nitrogenatmosphere and with continuous stirring. A total of about 0.46 g ofsodium metal is then added to the mixture resulting in the formation ofa soluble blue-colored product on the metal which diffuses into the bulksolution. This product is identified as the anthracene radical-anionform and has visible absorbance peaks at 726, 698, 656, 594 and 548 nm.After the Na dissolves, a piece of Teflon PFA (perfluoralkoxy) film (2mil thick) is immersed in the NaAn solution for about 2 minutes. Thistreatment results in causing substantial darkening of the PFA surface,indicative of chemical surface modification.

EXAMPLE 15

A NaAn solution is prepared as described in Example 14. A piece ofRO2800® (PTFE film with filler) is immersed in the NaAn (radical-anioncomplex) bath for about 3 minutes, then rinsed with acetonitrile,followed by dipping in a 5 mM PdCl₂ /ACN solution for 1 minute to give aPd surface deposit. On placing the Pd seeded sample in a conventionalelectroless Cu plating bath for about 3 minutes, a continuous Cu depositis formed on the RO2800 substrate surface.

EXAMPLE 16

A NaAn solution is prepared as described in Example 14. About 20 ml ofthe NaAn/THF solution is added to about 20 ml of NMP solvent with novisible reaction or color change occurring. The NaAn is stable in thismixture since it is able to instantly darken the surface of PTFE onexposure.

The PTFE sample is immersed in the NaAn solution for about 5 minutes,then subjected to Pd metal seeding and electroless Cu plating asdescribed in Example 15 with similar metallization results.

EXAMPLE 17

A NaAn solution is prepared as follows:

To about 500 ml of anhydrous tetrahydrofuran is added about 4.45 g ofanthracene (0.05M) and magnetically stirred for 15 minutes in a nitrogenglove box. About 1.04 g freshly cut sodium metal is thoroughly rinsedwith anhydrous THF solvent and then added to the anthracene/THFsolution. The characteristic blue color of the anthracene radical-anionstreams from the Na particles. This solution is kept stirring for 24hours before used as a reducing bath. A sample of PTFE measuring 4 cm×4cm×0.5 cm is immersed in the sodium anthracene (radical-anion complex)solution for 5 minutes, then rinsed with THF and Pd seeded as in Example8. A highly reflective, electrically continuous electroless Cu film isformed on the PTFE surface by plating as described in Example 1.

EXAMPLE 18

A lithium anthracene anthracene (LiAn) solution is prepared as describedin Example 17 using lithium metal shavings instead of Na to generatelithium anthracene complex in THF. The LiAn complex in solution exhibitsabsorbance peak maxima at 732, 698, 656, 596 and 548 nm. A sample ofPTFE is treated in this bath and Pd seeded and electroless Cusubsequently plated as described in Example 17 with similar results. Asample of Teflon PFA is also treated in the LiAn solution and seeded andCu plated.

EXAMPLE 19

A potassium anthracene (KAn) solution is prepared as described inExample 17 using potassium metal instead of Na to generate potassiumanthracene complex reducing bath. A sample of PTFE is treated in thisbath and Pd seeded and electroless Cu subsequently plated as describedin Example 17 with similar results.

EXAMPLE 20

A potassium anthracene solution is prepared by adding about 17.8 gm ofanthracene to about 500 ml of ethylene glycol dimethyl ether (monoglyme)in a flask in a glove box. A total of about 3.8 gm potassium metal isthen added to the mixture. This composition gives a 5% by weight KAnsolution. The mixture is then stirred overnight to allow the KAnformation to complete. The solution is then brought out of the glove boxand placed into a large glass vessel blanketed with Ar gas. The batheffectiveness in modifying the surface of RO2800 samples wasperiodically tested. The experiment is terminated after 90 hours withthe solution still being active.

EXAMPLE 21

A 5% by weight KAn solution is prepared as in Example 20 above anddiluted 4:1 with NMP to yield a 1% KAn solution (80% NMP). This mixtureis stable and capable of reducing PTFE samples as demonstrated by thesurface darkening upon exposure to the solution.

EXAMPLE 22

A KAn solution is prepared as described in Example 20. The monoglyme isallowed to evaporate and the solid potassium anthracide complexcollected. The melting point of the potassium anthracide crystalsis >300° C. The dark-blue crystals turn white on exposure to air as aresult of the radical-anion oxidation. Potassium anthracene salt isadded to a solution of anhydrous NMP to give a 0.05M anthraceneradical-anion solution resulting in the characteristic deep blue-blackcoloration of the solution. The KAn is stable in NMP. A sample of PTFEis treated in this bath and Pd seeded and electroless Cu subsequentlyplated as described in Example 17 with similar results.

EXAMPLE 23

A 25% by weight KAn (1.02 Molar) THF solution is prepared by addingabout 290.4 gm anthracene and about 63.5 gm K metal to about 1600 ml ofTHF. About 500 to 600 ml portions of the dissolved KAn/THF solution areremoved from the glove box and rotory evaporated under reduced pressurein a chemical hood. A blue colored crystalline solid remains after thesolvent is removed. About 270 gm of the KAn solid is then added to aglass tank containing about 2300 ml of NMP solvent under ambientconditions. After the addition, the solution is blanketed with a N₂ gasand a non hermetic aluminum foil cover. The activity of the bath ischecked periodically by immersing PTFE and RO2800 samples for about 15seconds and noting whether any surface modification (darkening) occurs.The bath is effective after 1000 hours, with no evidence of any loss inreducing power.

EXAMPLE 24

A NaAn/NMP solution is prepared using the procedure of Example 22. Asample of PTFE is treated in this bath and Pd seeded and electroless Cuplated with similar results as for Example 17.

EXAMPLE 25

A benzophenone radical-anion solution is prepared as in Example 15 usingabout 4.55 g benzophenone instead of anthracene to generate a sodiumbenzophenone radical-anion complex/THF solution. A sample of PTFE istreated in this bath and Pd seeded and electroless Cu subsequentlyplated as described in Example 17 with similar results.

EXAMPLE 26

A potassium benzophenone complex and NMP solution is prepared asdescribed in Example 20 for KAn synthesis. This mixture is stable andcapable of reducing PTFE samples. PTFE, PFE and RO2800 samples treatedin this bath and Pd seeded followed by electroless Cu plating asdescribed in Example 17 yielded similar results.

EXAMPLE 27

A piece of Teflon PTFE is immersed in Tetra-Etch® (W. L. Gore, Inc.)solution (sodium naphthalide) for 1 minute, then rinsed with monoglyme,followed by immersing into 5 mM PdCl₂ /ACN solution. The sample whenexposed to an electroless Cu plating solution deposited a bright,uniform Cu layer onto the surface, indicating Pd seeding in prior steps.

EXAMPLE 28

A potassium phenanthridine (radical-anion complex) solution is preparedby adding about 3.5 g phenanthridine and about 0.75 g potassium metal toabout 20 ml of monoglyme yielding a red-colored product. A sample ofPTFE, PFA and RO2800 each immersed for 3 minutes in this bath showsurface discoloration indicative of chemical modification as discussedhereinabove.

EXAMPLE 29

An anthracene/DMF reducing solution is prepared as detailed inExample 1. A PTFE substrate measuring 5 cm×5 cm×165 mils thick andcontaining drilled through holes having 18 mils diameter or an aspectratio of 9.16-to-1 is exposed to the reducing bath for 10 minutes withconstant agitation of the substrate to promote solution flow through thevias. After reduction, the substrate is Pd seeded as described inExample 8 and electrolytically plated using acid Cu sulfate bath asdescribed in Example 1. Photomicrographic analysis of through hole crosssections shows uniform and complete Cu coverage of the plated throughholes.

EXAMPLE 30

A electrolyte solution consisting of 0.1M tetrabutyl-ammoniumfluoroborate in N,N'-dimethylformamide is placed in a flat dish underambient conditions and allowed to saturate with oxygen. The cathode(working) electrode consists of a stainless steel rod (2 mm dia) that isinsulated except for the flat end. A Pt wire is used as the counter(anode) electrode and both electrodes are maintained in the electrolytesolution without use of separate compartments. A constant current of 10mA is applied to the electrodes. A piece of pure polytetrafluoroethyleneis placed at the bottom of the cell and is then contacted with thecathode electrode. The polytetrafluoroethylene surface at the pointelectrode contact instantly is discolored resulting in a blackappearance. The region which became black (modified) is confined to theelectrode contact area. However, extended contact causes "spreading" ofthe black area, i.e., further surface modification extending from thecontact point. Moving the electrode along the polymeric surface causessurface modification along all contact points and a black image isgenerated across the surface using a "writing" motion. Those regionswhich has been modified show excellent wettability on exposure todistilled water.

EXAMPLE 31

An electrolyte solution and electrochemical arrangement as describedabove in example 1 is assembled in a nitrogen glove box.Polytetrafluoroethylene and RO2800 (glass/ceramic filledpolytetrafluoroethylene) samples are selectively reduced as defined inExample 21.

After the patterned surface modifications are made, the samples areimmersed in an N-methyl-2-pyrrolidone solution containing about 5 mMPdCl₂ for about 30 seconds to deposit palladium metal.

The samples are then exposed to an electroless copper plating bath asdescribed in Example 1 resulting in copper deposition only on thoseregions that are selectively reduced. The Cu deposits adhere quite welland are electrically continuous across the modified surface regions.Isolated metal patterns are not shorted.

EXAMPLE 32

A electrolyte solution consisting of 0.1M TBAFB in DMF is placed in aflat dish inside of a nitrogen filled glove box. A piece of PTFEmeasuring 4 cm×4 cm×0.7 cm is immersed into the electrolyte bath andheld in place by a supporting fixture. The electrochemical circuit iscomprised of a Pt mesh anode and a hand-held drill with 1.5 mm dia. bitis connected to the power supply to function as the cathode. A constantcurrent of 10 mA is applied to the drill bit while several through holesare formed in the PTFE substrate. The substrate is then removed and Pdseeded as described in Example 8 which results in a uniform Cu depositon the walls of the drilled holes.

What is claimed is:
 1. A method of treating a halogenatedpolymeric-containing substrate, comprising the steps of:exposing atleast portions of said halogenated polymeric-containing substrate to acomposition containing a reducing agent and an aprotic solvent selectedfrom the group consisting of nitriles, nitro compounds, amides, esters,carbonates, oxides, sulfo compounds and mixtures thereof, wherein saidsolvent is free of ethers, amines, ammonia, and wherein said compositionis prepared by reacting a metal with an organic compound selected fromthe group consisting of polyaryl compounds, aromatic carbonyl containingcompounds, aromatic nitriles, and aromatic heterocyclic nitrogencontaining compounds in a reaction solvent which does not react withsaid metal but permits reaction between said metal and said organiccompound to thereby provide said reducing agent, isolating said reducingagent from said reaction solvent to obtain a reaction product as asolid, adding said reaction product to said aprotic solvent; andcontacting said treated substrate with a material to promote adhesion ofsaid material to said treated surface.
 2. A method according to claim 1,wherein said aprotic solvent is selected from the group consisting ofcyclic amides and cyclic esters.
 3. The method of claim 1 wherein, saidreducing agent is formed form a neutral organic compound that is atleast one specie selected from the group consisting of carbodiimides andquaternary aromatic nitrogen compounds.
 4. The method of claim 1 whereinsaid chemical reducing agent is a neutral organic or organometalliccompound whereby all or a portion of the said neutral organic compoundhas been electrochemically reduced in an aprotic solvent containing asupporting electrolyte salt.
 5. The method of claim 1 wherein saidhalogenated polymeric material containing substrate is a free-standingor supported film of a polymer selected from the group consisting ofpoly(tetrafluoroethylene), copolymers of tetrafluoroethylene andhexafluoropropylene, polytrifluorochloroethylene, copolymers oftetrafluoroethylene and an olefin, copolymers of trifluorochloroethyleneand an olefin, copolymer of tetrafluoroethylene and polyperfluoroalkoxyresin, polyvinyl fluoride, polyvinylidene fluoride, polyvinyl chloride,polyvinylidene chloride, copolymer of poly(tetrafluoro)ethylene andpoly(di-trifluoromethyl(dioxole difluoro)ethylene, and mixtures thereof.6. The method of claim 1 wherein said halogenated polymericmaterial-containing substrate has a thickness of about 100 angstroms to5 mils.
 7. The method of claim 4 wherein, said aprotic solvent is atleast one member selected from the group consisting of cyclic amides andcyclic esters.
 8. The method of claim 1 wherein the said chemicalreducing agent is an organic or organometallic compound whereby all or aportion of the said organic or organometallic compound has beenchemically reduced by an alkali or alkaline earth metal.
 9. The methodof claim 1 wherein said reducing agent is formed form a neutral organiccompound that is at least one specie selected from the group consistingof unsaturated aromatic hydrocarbons, aromatic carbonyl compounds,imides, diimides, nitriles, anhydrides, quitones, aromatic heterocyclicnitrogen compounds, azomethines, immonium salts, azo compounds, amineoxides, nitro and nitroso compounds and organometallic compounds. 10.The method of claim 1 wherein said reducing agent is selected from thegroup consisting of anthracene radical-anion, 9,10-diphenylanthraceneradical anion, benzophenone anign, anthraquinone anion,N-N-butylphthalimide anion, phthalonitrile anion, acridine anion,trans-stilbene anion, naphthalene radical-anion, phenanthridineradical-anion, perylene radical anion and ruthenium (tribipyridyl)diperchlorate.
 11. The method of claim 10 wherein a cation of saidreducing agent is at least one member selected from the group consistingof tetraalkylammonium, tetraalkylphosphonium, alkali metal, mixedalkyl-aryl ammonium, mixed alkyl-aryl phosphonium, or chelated metal.12. The method of claim 4 wherein said supporting electrolyte saltcontains a cation which is at least one member of the group consistingof tetraalkylammonium, tetraalkylphosphonium, alkali metal, mixedalkyl-aryl ammonium, mixed alkyl-aryl phosphonium, or chelated metal andsaid supporting electrolyte salt contains an anion that is at least onemember selected from the group consisting of tetrafluoroborate,hexafluorophosphate, perchlorate, halide, aryl sulfonate, and aromaticorganic compounds.
 13. The method of claim 4 wherein said supportingelectrolyte salt contains at least one member selected from the groupconsisting of tetrabutylammonium tetrafluoroborate, tetraethylammoniumtetrafluoroborate, tetrabutylammonium hexafluorophosphate,tetraethylammonium bromide, lithium tetrafluoroborate, lithiumperchlorate, benzyltributylammonium tetrafluoroborate, potassiumanthracene, and sodium naphthalenene.
 14. The method of claim 4 whereinsaid aprotic solvent is at least one member selected from the groupconsisting of nitriles, nitro compounds, amides, amines, esters, ethers,carbonates, oxides, and sulfo compounds.
 15. The method of claim 1wherein said metal is a metal cation metal or metal complex wherein saidmetal is selected from the group consisting of palladium, platinum,ruthenium, silver, gold, copper, nickel, cobalt, and tin.
 16. The methodof claim 15 wherein said metal complex is selected from the groupconsisting of PdCl₂, PdBr₂, Pd(ACN)₂ Ci₂ CuBF₄, CuIP(OCH₃)₃, AgBF₄,NiBr₂, CoCl₂.
 17. The method of claim 14 wherein said metal is at adepth no greater than 2000 angstroms below the surface of saidhalogenated polymeric material containing substrate.
 18. The method ofclaim 2 wherein said metals are at a depth no greater than 800 angstromsbelow the surface of said polymeric material.
 19. The method of claim 1wherein said metal is at a depth no greater than 200 angstroms below thesurface of said halogenated polymeric material containing substrate. 20.The method of claim 1 wherein said reducing agent is prepared byreacting a metal with an organic compound to form a reaction product,said organic compound is selected from the group consisting of polyarylcompounds, aromatic carbonyl containing compounds, aromatic nitriles anaromatic heterocyclic nitrogen containing compounds in a solvent whichdoes not react with said metal but permits reaction between said metaland said organic compound.
 21. The method of claim 20 wherein said metalis an alkali metal.
 22. The method of claim 21 wherein said organiccompound is selected from the group consisting of anthracene,9,10-diphenylanthracene, benzophenone, phenanthridine, phthalonitrile,perylene and fluorene.
 23. The method of claim 20 wherein the reducingagent is isolated from said solvent to obtain the reaction product incrystalline form.
 24. The method of claim 23 wherein said reactionproduct is added to a solvent for contacting with said substrate. 25.The method of claim 24 wherein said solvent is selected from the groupof N-methyl-2-pyrrolidone, N,N-dimethylformamide, acetonitrile andpropylene carbonate.
 26. The method of claim 24 wherein said solvent isfree of ether and amine.
 27. The method of claim 1 wherein said metal isan alkali metal.
 28. The method of claim 27 wherein said organiccompound is the group consisting of anthracene, 9,10-diphenylanthracene,selected from benzophenone, phenanthridine, phthalonitrile, perylene andfluorene.
 29. The method of claim 1 wherein said aprotic solvent isselected from the group consisting of N-methyl-2-pyrrolidone,N,N-dimethylformamide, dimethyl sulfoxide, acetonitrile and propylenecarbonate.
 30. The method of claim 1 wherein said reaction solvent isselected from the group consisting of ammonia, ethers and amines.
 31. Amethod according to claim 1 wherein said material is selected from thegroup consisting of a metal, a polymer, a glass, wood, a ceramic and aglass ceramic.
 32. A method according to claim 27 further includingcontacting said halogenated polymeric surface with another material topromote adhesion of said other material to said treated surface.
 33. Amethod according to claim 32 wherein said material is selected from thegroup consisting of a metal, a polymer, a glass, wood, a ceramic and aglass ceramic.